Adjustable volume pipettes and syringes have been wellknown for many years. These devices usually include means for adjusting the stroke of the plunger shaft or plunger within the pipette barrel to precisely calibrate the pipette volumetric capacity. For example, U.S. Pat. Nos. 2,530,909 to Riggs; 3,815,790 to Allen et al; and 4,084,730 to Franke et al all disclose adjustable volume pipetting devices having stop means to limit the travel of the plunger shaft thereby varying the pipette volumetric capacity. While these above-mentioned pipetting devices may vary the volume of liquid or reagent to be dispensed therefrom, the stop means will prevent complete downward axial displacement of the plunger shaft towards the dispensing end of the barrel. These structural arrangements thereby permit spaces to exist between the plunger and the dispensing end of the barrel, causing slight inaccuracies in the volume of liquid samples to be dispensed, providing non-positive displacement.
Attempts have been made to vary the size of the barrel by using a threadedly engaging sleeve extension. For example, U.S. Pat. No. 3,232,117 to Gilmont and U.S. Pat. No. 4,098,125 to Lee both show adjustable volume pipetting devices which include means to vary the volume capacity of the barrel by providing a threadedly engaging sleeve or extension thereto. However, these devices employ relatively complex and expensive structures for facilitating extension or contraction of the pipette barrel.
In recent years, attempts have been made to insure precise and uncontaminated pipette sampling by adding disposable tube tips to the barrel dispensing end, which tips receive samples therein without contacting the pipette plunger chamber. Samples are discharged through the tips by positive displacement of the plunger. For example, U.S. Pat. Nos. 4,023,716 and 4,165,646 to Shapiro both disclose sampling pipettes which include the use of disposable tips attached to the pipette barrel dispensing end for incorporating a non-contaminated environment for storing liquid samples.
No adjustable volume pipette sampler or syringe especially adapted for use with accessories has previously been available which will enable quick, simple and inexpensive sampling of liquids with precision and greater assurance of absence of contamination. There is a greatly need for an adjustable volume pipetting device, especially one with two colinear and relatively adjustable barrels, which will permit easy attachment of accessories, such as filtering devices and/or disposable high volume capacity reservoirs. Additionally, an adjustable volume pipette sampler or syringe capable of using either positive or air displacement would great benefit the bio-engineering (and other like science) sample testing industries. Furthermore, there is a need for coupling means to attach the various accessories to the pipetting device, especially in instances where high pressure is desired, such as is required in high pressure liquid chromatography (HPLC).